Oblique drawing is an effective method to make spatial geometry intuitive, and it is the drawing basis of spatial geometry intuitive. Its formula is: parallelism is still vertical to oblique, horizontal and vertical and semi-vertical; Seeing is believing, covering is virtual, and the sense of space is well reflected.

It is known that the line segment parallel to the Y axis in the figure is drawn parallel to the Y' axis in the orthographic drawing, and its length is half of the original one. The area of oblique double-sided drawing is √2/4 times that of the original drawing.